Field
Various communication services may benefit from an identifier that can correlate a user equipment or a packet data network connection with a particular cell or area. For example, a correlation identifier may be useful to address management of user plane congestion (to identify which devices are located in a congested cell).
Description of the Related Art
The Evolved Packet System (EPS) provides a new radio interface and a new packet core network functions for broadband wireless data access. The EPS core network (or IP-CAN) can include the Mobility Management Entity (MME), packet data network gateway (P-GW) and serving gateway (S-GW).
FIG. 1 illustrates an overall PCC architecture. For a more complete discussion of this architecture, see 3GPP TS 23.203, which is hereby incorporated herein by reference in its entirety.
The Policy Charging Control (PCC) architecture, including deep packet inspection (DPI) functionality in traffic detection function (TDF) and policy and charging enforcement function (PCEF) enhanced with application detection and control (ADC) rules, extends the architecture of an IP-CAN, where the PCEF is a functional entity in the gateway node, such as a P-GW or gateway general packet radio service (GPRS) support node (GGSN), providing the IP access to the packet data network (PDN).
System requirements for user plane congestion management (UPCON) are described in 3GPP TS 22.101, which is hereby incorporated herein by reference in its entirety. 3GPP TR 23.705 (which is also hereby incorporated herein by reference in its entirety) documents an agreement to follow a so-called core network (CN) based solution by which congestion information from the radio access network (RAN) is used in the Core to perform congestion mitigation.
FIG. 2 illustrates an UPCON control loop. A logical function, the RAN congestion awareness function (RCAF), is defined. The RCAF collects operations, administration and maintenance (OAM)-based non-real-time RAN user plane congestion status per eNB or radio cell, and generates congestion indications towards the core network including affected subscribers. Two new reference points are introduced: between RCAF and MME/SGSN to get the affected subscribers (in terms of their international mobile subscriber identities (IMSIs)) in a cell, and between the RCAF and PCRF to pass on the combined RAN user plane congestion status to the PCRF. The approach may permit per-UE/bearer policy decisions to be taken by the PCRF.
FIG. 3 illustrates a reference architecture for RAN user plane congestion detection and reporting. For a more complete discussion of this architecture, see 3GPP TS 23.203. The interface between RAN's OAM system and the RCAF is not specified, while the interfaces between MME/SGSN and RCAF (Nq and Nq′) are specified in 3GPP TS 23.401 and 3GPP TS 23.060 and enable the RCAF to retrieve the list of UEs (respectively their IMSIs), which are currently camping in congested cells as reported by RAN's OAM system. The PCRF receives RAN User Plane Congestion Information reports (called RUCI) from the RCAF via Np as another input for policy decisions as described in section 6.2.1.1 of 3GPP TS 23.203. Each of 3GPP TS 23.401 and 3GPP TS 23.060 is hereby incorporated herein by reference in its entirety.
The PCRF performs congestion mitigation actions on a per UE basis. Thus, the PCRF may require information regarding which UEs are in congested cells, before making policy decisions.
The OAM RAN system is configured to provide on a regular basis a list of congested cells to the RCAF. The list does not provide identities of UEs that are camping in those cells. Thus, conventionally the RCAF cannot simply forward the list of congested cells towards the PCRF, as the PCRF is unaware which UEs are in which cells. PCRF acts on a per UE and not on a per cell or location area basis.
Conventionally, only RAN nodes, such as eNBs, are aware which UEs are in which cells.
3GPP decided that RCAF needs to query MME/SGSN for identities of UEs camping in congested cells. In turn, MME/SGSN queries the eNB/RNC for current location of UEs.
Once RCAF has identified which UEs are impacted by congestion, it informs the PCRF via RUCI reports. PCRF in turn executes congestion mitigation measures on a per UE basis.
The E-UTRAN cell global identifier (ECGI) stored in the MME may be obsolete information as the eNB is not required to inform the MME/SGSN about all cell changes. Intra-eNB cell changes, such as handovers between cells hosted by the same eNB, do not require that MME/SGSN be informed about such a cell change. Also inter-eNB handover, so-called X2 handovers where two eNBs have a direct signalling connection, do not necessarily require that MME/SGSN be informed by RAN.
As MME/SGSN are not always up-to-date regarding the cell via which a UE is currently connected to the network, the query sent by the RCAF containing congested cells and the response sent by MME/SGSN back to RCAF may provide wrong results, which implies that UEs currently camping in a non-congested cell may erroneously suffer from congestion mitigation measures. Or the other way around, UEs camping in a congested cell but assumed by the MME/SGSN as being in a non-congested cell, can continue generating huge amount of traffic and so prolonging the congestion state of the cell.
On top of that it can be questioned whether the current solution envisaged by 3GPP that RCAFs have to query MMEs/SGSNs for identifying the impacted UEs is the best approach. The current solution assumes that RCAF compares existing congestion information with information in a new report received from RAN OAM, performing a new query towards MME/SGSN.
As stated above, the solution that RCAF queries the MME/SGSN to retrieve IMSIs of UEs camping in congested cells raises some issues. First, the current location of the UE is not always known accurately by the MME/SGSN as the RAN does not report all cell changes to the core network. Second, the solution requires introducing new interfaces between RCAF and MME/SGSN, which raises backward compatibility issues and increases the complexity in the network and the whole solution. Third, the solution requires that MME/SGSN are searching through their whole context data table with cell ID as search key just to find a probably small number of affected UEs and return the corresponding IMSIs. Fourth, the new functional entity RCAF and other entities involved in this solution (RAN OAM, MME/SGSN, PCRF) have to store context information (either per cell, per UE or both). The RCAF needs to correlate cell ID, TAI, IMSI and PCRF data.
In summary, an issue with the UPCON solution as described above is the missing direct correlation link between information available in PCRF based on user identities like IMSI and information available in RAN nodes (eNBs) based on cell IDs. For security reasons the IMSI cannot be sent to RAN, thus cannot be used as correlation ID. As a consequence the UPCON solution requires that new interfaces towards MME/SGSN are introduced just for the sake to provide a mapping between cell ID and IMSI.
Although there may be other ways of identifying PDN connections, these other ways may not address the above-identified issues. For example, solutions related to proxy mobile IP (PMIP) and a situation of identifying one connection out of multiple PDN connections to the same APN may not have relevance in E-UTRAN. This may be because an APN may have no meaning or relevance in the radio network. Moreover, PMIP may only pertain to S5/S8.